Understanding the mechanism of hemoglobin dissociation and association is a fundamental factor to study hemoglobin stability and production of hemoglobin based extracellular oxygen carriers. Clinical studies with different crosslinked and modified hemoglobins reveled symptoms which are due to fast kidney filtration and accelerated autoxidation. We are utilizing ultrafast time-resolved intrinsic tryptophan fluorescence for monitoring the hemoglobin dissociation into the dimers and monomers under high hydrostatic pressure. Our study include native human hemoglobin as well as crosslinked and mutated human and bovine hemoglobins.